The problem of scanning transmission lines occurs, for instance, in communication controllers as described in European Patent EP-A-0.077.863 (FIG. 1). Communication controllers are connected to a plurality of user's terminals or devices T through line adapters. Those line adapters are connected to several transmission lines by scanning means which perform the cyclic scanning of the data and control slots provided on the different lines. A given line adapter includes a plurality of Line Interface Couplers (LIC) as described in said patent EP-A-0.077.863, each of which is connected to users terminals or devices through several serial lines operated at various speeds.
Generally, in a communications controller like the IBM 3725 controller, each LIC which is physically plugged to the scanner (front end scanner or FES in said patent) is scanned, even if inactive. This wastes time and throughput when a given line adapter is not connected to the allowed maximum number of active lines. For instance, if each line adapter can support 8 LICs, LIC0 to LIC7) each LIC supporting four 56 KBPS lines, and if LIC0 and LIC7 are the only active LICS, the scanning of the lines is nevertheless performed from LIC0 to LIC7, including inactive LICS 1 to 6. Furthermore, if the throughput of the line adapter is entirely dedicated to the scanning of one high speed line (256 kbps), this line has necessarily to be connected to the LIC having the physical or wired adress 0 on the line adapter in order to reduce the scanning time to a minimum. Consequently, lines have to be unplugged at each configuration change by the user. This is likely to generate much trouble and hardware difficulties.
Besides, according to the known scanning scheme, the cost of the necessary hardware rises rapidly if several high speed lines have to be scanned: even if they are not simultaneously activated, they cannot be simultaneously connected to the same line adapter, and thus more line adapters are needed.